The study was published in the May edition of Archives of General
Psychiatry.

Children who were breastfed longer scored higher on average at age 6 1/2
years in verbal intelligence, nonverbal intelligence, and overall intelligence,
Kramer finds. Teachers rated them higher in reading and writing than children
who weren't breastfed as long or as exclusively.

"Prolonged and exclusive breastfeeding makes kids smarter," Kramer
tells WebMD. "I would say as a target for mothers, if they could
exclusively breastfeed for three months and continue to breastfeed for some
degree for one year, that would be good."

Breastfeeding exclusively [with no formula supplements] for six months would
be even better, Kramer says. But he concedes that is difficult for many women,
especially if they return to work.

Breastfeeding and IQ: Studying the Data

A host of studies have looked at breastfeeding and IQ. "Most of the
studies have found an association between breastfeeding and higher IQ,"
Kramer tells WebMD. But most have been what scientists call observational
studies, with children whose mothers chose to breastfeed compared with those
children whose mothers chose not to.

Kramer and others say these studies may be affected by differences in the
way moms who breastfeed interact with their children and those who don't.

Kramer and his colleagues looked at almost 14,000 children in Belarus
who visited 31 hospitals and clinics there. The participants are part of the
large-scale study known as the Promotion of Breastfeeding Intervention Trial
(PROBIT). The researchers assigned half to an intervention that
encouraged them to breastfeed exclusively long term or to another group that
got the usual maternity care and child care.

This approach is considered more feasible and ethical than assigning mothers
to breastfeed or bottle-feed.

"Those who got the breastfeeding intervention breastfed longer and more
exclusively," Kramer says. The number of mothers still breastfeeding
exclusively at three months was seven times higher in the intervention group of
mothers -- 43% compared to 6% of those who didn't get the intervention.